By the late 1950s the intelligence branches of the United States Army, Navy and Air Force operated largely independently of one another, frequently producing overlapping or contradictory assessments that frustrated the Secretary of Defense and the Joint Chiefs of Staff, a fragmentation Cold War planners increasingly viewed as dangerous given the speed and stakes of nuclear era decision making.
Secretary of Defense Robert McNamara, newly appointed under President John F. Kennedy, ordered the creation of a single Defense Intelligence Agency in August 1961 to absorb and coordinate the service intelligence staffs' analytical functions, and the Agency stood up formally on 1 October 1961 under Department of Defense Directive 5105.21.
The DIA was structured to serve the Secretary of Defense, the Joint Chiefs of Staff and military commanders directly, producing centralized military intelligence assessments while the individual services retained their own tactical and operational intelligence units, a division of labor periodically renegotiated as the Agency's role expanded through the Cold War and after the September 11 attacks. Its founding placed it institutionally alongside, but organizationally separate from, the civilian Central Intelligence Agency, with which it would later share responsibility for one of the Cold War's more unusual joint research efforts.